Gaseous Exchange, Electricity & Pathogenic Diseases: quick revision, 20 bites

Gaseous Exchange Happens by Diffusion, Not Breathing

Breathing moves air — diffusion moves oxygen.

Breathing (ventilation) only brings air to the lungs. The actual **exchange of gases** happens by **diffusion** across the alveolar membrane.

Takeaway. Breathing is mechanical; gaseous exchange is passive diffusion across alveoli.

Key Terms in Human Gaseous Exchange

Master these terms before the exam.

Takeaway. Alveoli + haemoglobin + diffusion = the core machinery of gas exchange.

Path of Oxygen: Air to Cell

Follow the oxygen molecule's journey.

Each step relies on **concentration gradients** — O₂ always moves from where it is more to where it is less.

Takeaway. Oxygen travels nose → trachea → bronchi → alveoli → blood → cells.

Alveoli: Built for Maximum Diffusion

300 million tiny balloons in your chest.

Takeaway. Large surface area + thin walls + rich blood supply = efficient gas exchange.

Breathing ≠ Respiration

These two are NOT the same thing.

Takeaway. Breathing is physical; respiration is biochemical energy release.

Electric Current: Flow of Charge

Electricity is just electrons on the move.

**Electric current** is the rate of flow of electric charge through a conductor. It flows from the negative terminal to the positive terminal inside a circuit (opposite to conventional current).

Takeaway. Current = charge flowing per second, measured in amperes.

Ohm's Law: The Backbone of Circuits

One equation rules every circuit.

Takeaway. V = IR links voltage, current and resistance in every circuit.

Voltage, Current & Resistance Defined

Three pillars of every circuit.

Takeaway. Voltage pushes, current flows, resistance opposes.

Series vs Parallel Circuits

Same components, very different behaviour.

Takeaway. Series shares current; parallel shares voltage.

Why Household Wiring Uses Parallel Circuits

Your home runs on parallel — here's why.

Takeaway. Parallel wiring = independent devices + full voltage to each.

Don't Confuse Current and Voltage

Current isn't 'pushed' — voltage is.

Takeaway. Voltage drives; current results.

Pathogens: Microbes That Cause Disease

Not all microbes are friendly.

**Pathogens** are disease-causing microorganisms. They enter the body, multiply, and disrupt normal function — causing **pathogenic diseases** (also called infectious or communicable diseases).

Takeaway. Pathogens = disease-causing microbes; they spread and multiply inside hosts.

Four Types of Pathogens & Their Diseases

Four culprits, many diseases.

Takeaway. Bacteria, viruses, fungi and protozoa each cause distinct diseases.

How Pathogens Spread

Five common routes of infection.

Takeaway. Knowing the route of spread is the first step to prevention.

Antibiotics Don't Kill Viruses

Antibiotics are useless against colds.

Takeaway. Antibiotics = bacteria only. Viruses need different treatment.

Exam Tip: Link Cause to Prevention

Examiners love cause-and-prevention pairs.

Takeaway. Always pair a disease with its pathogen AND its prevention method.

Remember the Four Pathogen Types

B-V-F-P: the pathogen family.

Use **B-V-F-P** to recall the four pathogen types: **B**acteria, **V**iruses, **F**ungi, **P**rotozoa.

Takeaway. B-V-F-P = the four pathogen groups.

Your Lungs Handle ~11,000 Litres of Air Daily

Your lungs never take a day off.

An average adult breathes about **11,000 litres of air per day** — and the alveoli process oxygen and carbon dioxide continuously without conscious effort.

Takeaway. Alveoli work non-stop, processing thousands of litres of air daily.

Electricity in Medical Devices

Electricity keeps hospitals alive.

Takeaway. Ohm's law and circuits power life-saving medical technology.

Where These Topics Lead

From classroom to career.

Takeaway. These three topics open doors to medicine, engineering and public health careers.